internal/pkg: input iterator via IR cache

Primarily useful for garbage collection.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/ir.go

@@ -8,6 +8,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"iter"
 	"slices"
 	"strconv"
 	"sync"
@@ -65,6 +66,18 @@ func NewIR() *IRCache {
 	return &IRCache{zeroIRCache()}
 }
 
+// Inputs returns an iterator over direct and transitive inputs of an [Artifact]
+// in randomised order.
+func Inputs(a Artifact) iter.Seq2[Artifact, unique.Handle[ID]] {
+	ic := NewIR()
+	ic.Ident(a)
+	return func(yield func(Artifact, unique.Handle[ID]) bool) {
+		ic.artifact.Range(func(key, value any) bool {
+			return yield(key.(Artifact), value.(unique.Handle[ID]))
+		})
+	}
+}
+
 // IContext is passed to [Artifact.Params] and provides methods for writing
 // values to the IR writer. It does not expose the underlying [io.Writer].
 //